JP4556749B2 - Light guide plate and display device - Google Patents

Light guide plate and display device Download PDF

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JP4556749B2
JP4556749B2 JP2005111750A JP2005111750A JP4556749B2 JP 4556749 B2 JP4556749 B2 JP 4556749B2 JP 2005111750 A JP2005111750 A JP 2005111750A JP 2005111750 A JP2005111750 A JP 2005111750A JP 4556749 B2 JP4556749 B2 JP 4556749B2
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light
guide plate
light guide
diffraction grating
light source
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JP2006294361A (en
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恵理 宮本
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Toppan Inc
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本発明は、液晶表示装置に代表される表示装置に主として採用されるエッジライト方式のバックライト・ユニットに用いられる導光板の改良に関する。   The present invention relates to an improvement in a light guide plate used in an edge light type backlight unit mainly employed in a display device typified by a liquid crystal display device.

現在、広く普及している携帯電話や携帯情報端末では、照明装置として主にバックライト方式の照明装置（以下、背面照明装置とも称する）が用いられている。
このような背面照明装置としての光源は、高輝度でしかも輝度ムラがなく平面全体を照明する必要がある。
さらに、表示装置の大型化・薄型化の要求に伴って、導光板にも大型化・薄型化が求められている。 At present, cellular phones and personal digital assistants that are widely used mainly use backlight type illumination devices (hereinafter also referred to as back illumination devices) as illumination devices.
Such a light source as a back lighting device needs to illuminate the entire plane with high luminance and no luminance unevenness.
Further, along with the demand for larger and thinner display devices, the light guide plate is also required to be larger and thinner.

図１に一般的な背面照明装置の構成を示す。
この背面照明装置は、主に光源１，導光板２，反射シート４，拡散シート５，プリズムシート６からなっている。 FIG. 1 shows a configuration of a general backlight device.
This back lighting device mainly includes a light source 1, a light guide plate 2, a reflection sheet 4, a diffusion sheet 5, and a prism sheet 6.

光源としては、消費電力や実装スペースなどの点から主に発光ダイオード（ＬＥＤ）や冷陰極管ランプ（ＣＣＦＬ）が用いられ、これを透明樹脂からなる導光板の端面に配し、導光板に光を入射させることで、薄型化を実現している。   As the light source, a light emitting diode (LED) or a cold cathode tube lamp (CCFL) is mainly used in terms of power consumption and mounting space, and this is disposed on the end face of the light guide plate made of transparent resin, and light is applied to the light guide plate. Is made thin.

光源１からの光は、導光板２の端面から導光板２に入射する。
導光板２は、端面から入射した光を平面に広げて射出するための透明な板であり、主としてアクリル樹脂もしくはポリカーボネートが用いられる。
導光板２の裏面（もしくは、反対側の前面。あるいは、裏面・前面の双方。以下、裏面で代表して説明する。）には、ドットパターンもしくはプリズムパターンもしくは回折格子パターン３が形成されている。
導光板２に入射した光は、内部で全反射を繰り返して伝播していき、裏面のパターン３により、散乱もしくは反射もしくは回折して、導光板２の上面から射出される。
この際、導光板２に入射した光を均一に上面へ反射させて、導光板２の上面から射出する（画面内での輝度分布を均一化する）ための各種工夫が、裏面のパターン３には施されることが一般的である。 Light from the light source 1 enters the light guide plate 2 from the end face of the light guide plate 2.
The light guide plate 2 is a transparent plate for spreading the light incident from the end face and emitting it, and acrylic resin or polycarbonate is mainly used.
A dot pattern, a prism pattern, or a diffraction grating pattern 3 is formed on the back surface of the light guide plate 2 (or the front surface on the opposite side, or both the back surface and the front surface, which will be described below as a representative). .
The light incident on the light guide plate 2 propagates by repeating total reflection internally, and is scattered, reflected, or diffracted by the pattern 3 on the back surface and emitted from the upper surface of the light guide plate 2.
At this time, various measures for reflecting light incident on the light guide plate 2 uniformly on the upper surface and emitting it from the upper surface of the light guide plate 2 (making the luminance distribution in the screen uniform) are applied to the pattern 3 on the back surface. Is generally applied.

反射シート４は導光板３の裏面側に設けられ、導光板２の裏面から漏れた光を導光板２の方へ戻す働きをしている。   The reflection sheet 4 is provided on the back surface side of the light guide plate 3 and functions to return light leaking from the back surface of the light guide plate 2 toward the light guide plate 2.

拡散シート５は、導光板２の射出面側に設けられ、輝度の面内分布を均一化する役割を持っている。導光板２の上面にも拡散パターンが設けられていることが多く、拡散シート５とあわせて輝度ムラを低減させている。   The diffusion sheet 5 is provided on the exit surface side of the light guide plate 2 and has a role of making the in-plane distribution of luminance uniform. In many cases, a diffusion pattern is also provided on the upper surface of the light guide plate 2, and brightness unevenness is reduced together with the diffusion sheet 5.

プリズムシート６は、拡散シート５の上側に設けられ、拡散シート５から射出された光に指向性を持たせて射出面のピーク輝度を上げる働きをしている。また、拡散シート５から射出される光の進行方向を導光板の表面にほぼ垂直な方向へ揃える役割を果たしている。   The prism sheet 6 is provided on the upper side of the diffusion sheet 5 and functions to increase the peak luminance of the exit surface by imparting directivity to the light emitted from the diffusion sheet 5. Further, it plays the role of aligning the traveling direction of the light emitted from the diffusion sheet 5 in a direction substantially perpendicular to the surface of the light guide plate.

導光板２に入射した光を均一に上面へ反射させるための、導光板２の裏面に形成されるパターン３には、上述のように、ドットパターン，プリズムパターン，回折格子パターンなど各種形態があり、導光板の裏面にホログラムが形成されたタイプとして、特許文献１の提案が知られている。
特許文献１による導光板は、
透明板状体を備え、その一面にホログラムが設けられ、その板状体の一端の近傍に配置された光源から導入された光がその板状体中を繰り返し全反射しながら伝搬し、その伝搬される光の一部が前記ホログラムにより前記板状体の外部へ回折されるように構成されているホログラム導光板において、前記板状体の前記光源とは反対側の端部に前記の伝搬される光を吸収する吸収層が設けられていることを特徴とするホログラム導光板（請求項１）である。 The pattern 3 formed on the back surface of the light guide plate 2 for uniformly reflecting the light incident on the light guide plate 2 to the upper surface has various forms such as a dot pattern, a prism pattern, and a diffraction grating pattern as described above. As a type in which a hologram is formed on the back surface of the light guide plate, the proposal of Patent Document 1 is known.
The light guide plate according to Patent Document 1 is
A transparent plate is provided with a hologram on one side, and light introduced from a light source arranged near one end of the plate is propagated repeatedly and totally reflected in the plate. In the hologram light guide plate configured such that a part of the light to be diffracted by the hologram to the outside of the plate-like body, the light is propagated to the end of the plate-like body opposite to the light source. The hologram light guide plate is characterized in that an absorption layer for absorbing light is provided.

また、導光板の裏面に回折格子が形成されたタイプとして、
透明な板状体の少なくとも一端面から入射する光源からの光を、上記板状体の裏面に設けられた回折格子によって板状体の表面側へ回折させる導光板であって、
上記回折格子の断面形状または単位幅における格子部幅／非格子部幅の比の少なくとも１つが、上記導光板の表面における輝度が増大し、かつ均一化されるように変化せしめら
れていることを特徴とする導光板（特許文献２）のような提案も知られている。
特開２００２−１３１５５１号公報 特開平９−３２５２１８号公報 In addition, as a type in which a diffraction grating is formed on the back surface of the light guide plate,
A light guide plate that diffracts light from a light source incident from at least one end surface of a transparent plate-like body toward the surface of the plate-like body by a diffraction grating provided on the back surface of the plate-like body,
That at least one of the cross-sectional shape of the diffraction grating or the ratio of the grating part width / non-grating part width in the unit width is changed so that the luminance on the surface of the light guide plate increases and becomes uniform. A proposal such as a characteristic light guide plate (Patent Document 2) is also known.
JP 2002-131551 A JP-A-9-325218

背面照明装置（バックライト・ユニット）に要求される特性として、導光板の表面にほぼ垂直な方向から観察した際に、高輝度でしかも輝度ムラがなく導光板表面全体が光っていること、および薄型軽量であることが求められている。
しかしながら、従来の背面照明装置における導光板では、光源から導光板に入射する光のうちで最も強い成分である直進成分が終端面から抜けることによる正面方向における光の射出効率の低下、および端面における望ましくない反射によるノイズ光の発生が問題となることがある。
正面方向における光の射出効率は、背面照明装置としての光の利用効率であり、その低下は暗い照明装置を意味し、大きな問題である。 The characteristics required for the backlight unit (backlight unit) are that the entire surface of the light guide plate shines with high brightness and no luminance unevenness when observed from a direction substantially perpendicular to the surface of the light guide plate, and It is required to be thin and light.
However, in the light guide plate in the conventional backside illumination device, the light emission efficiency in the front direction decreases due to the straight component that is the strongest component of the light incident on the light guide plate from the light source coming out of the end surface, and in the end surface The generation of noise light due to undesirable reflections can be a problem.
The light emission efficiency in the front direction is the utilization efficiency of light as a back lighting device, and its reduction means a dark lighting device and is a big problem.

また、導光板の形状として、断面楔型のもの（光源に近い始端箇所から、光源に遠い終端箇所にかけて、徐々に厚みがテーパ状に減少する構造）とフラット構造のものがあり、従来は断面楔型が主流であったが、現在はフラット構造に主流が移りつつある。
断面楔形では、入射した光を端部まで比較的効率よく利用することができたが、フラット構造では、特に上記のような入射光の直進成分のロスが問題となる。 In addition, the light guide plate has a wedge-shaped section (a structure in which the thickness gradually decreases in a taper shape from a starting end position close to the light source to a terminal position far from the light source) and a flat structure. The wedge type was the mainstream, but now the mainstream is moving to a flat structure.
With the wedge-shaped cross section, incident light can be used relatively efficiently up to the end, but with the flat structure, the above-mentioned loss of the straight component of incident light becomes a problem.

上記特許文献２では、この問題を解決することが考慮されており、終端面に黒色の吸収層を設ける手法に係る記載がある。   In the above-mentioned Patent Document 2, it is considered to solve this problem, and there is a description relating to a method of providing a black absorption layer on the end face.

＜特許文献２ 段落００３３＞
図１に示したように、透明板状体２の光源４側と反対の他端２ｂに黒色塗料等からなる吸収層７を設けてこの他端２ｂに達する照明光５を吸収させて上記のような好ましくない戻り光５ｎの発生を防止するようにする。 <Patent Document 2 Paragraph 0033>
As shown in FIG. 1, an absorption layer 7 made of a black paint or the like is provided on the other end 2b opposite to the light source 4 side of the transparent plate-like body 2 to absorb the illumination light 5 reaching the other end 2b and Such an undesirable return light 5n is prevented from being generated.

特許文献２に記載の上記手法によれば、光の抜けおよび端面反射を防ぎ、ノイズの発生を抑制することができるが、光源からの照明光の利用効率は低下してしまうことに他ならず、表示装置による表示光の輝度向上には寄与しない。   According to the above-described method described in Patent Document 2, it is possible to prevent light leakage and end-face reflection and suppress the generation of noise. However, the use efficiency of illumination light from the light source is reduced. This does not contribute to the improvement of the brightness of the display light by the display device.

また、それを改善するために、単純に反射光量を増加させるべく、終端面に金属板もしくは金属蒸着を配置することによって、終端面からの光を反射させる手法も考えられるが、反射角を意図的に制御することは難しく、十分に光の利用効率を上げることができず、またノイズ光やムラの発生に起因するだけとなってしまう。   In order to improve it, a method of reflecting the light from the end surface by arranging a metal plate or metal vapor deposition on the end surface to simply increase the amount of reflected light can be considered, but the reflection angle is intended. It is difficult to control automatically, it is not possible to sufficiently increase the light use efficiency, and it is only caused by generation of noise light and unevenness.

本発明は、導光板の終端面における端面反射を適切に制御することで、ノイズ光の発生を抑えつつ、光の利用効率を上げ、高輝度の表示光を得ることを目的としている。   An object of the present invention is to appropriately control the end face reflection at the end face of the light guide plate, thereby suppressing the generation of noise light, increasing the light use efficiency, and obtaining high luminance display light.

上記の目的を達成するために、本発明による導光板は、
導光板の一方の端面に光源を配し、前記導光板に入射した光を均一に上面へ反射させて面光源とするエッジライト方式のバックライト・ユニットに用いられる導光板において、
光源と反対側の端面である終端面に、反射型回折格子を配置したことを特徴とする。 In order to achieve the above object, a light guide plate according to the present invention comprises:
In the light guide plate used in the edge light type backlight unit, a light source is arranged on one end surface of the light guide plate, and the light incident on the light guide plate is uniformly reflected on the upper surface to be a surface light source.
A reflection type diffraction grating is arranged on the end face which is the end face opposite to the light source.

本発明の導光板を用いたバックライト・ユニット（背面照明装置）では、導光板の終端面に回折格子パターンを配置することにより、導光板に入射した光の直進成分を導光板内の全反射光に変換することによって有効に利用することができ、光の利用効率を向上することが出来、高輝度の表示光が視覚可能な表示装置が得られる。   In the backlight unit (backlighting device) using the light guide plate of the present invention, a diffraction grating pattern is arranged on the end face of the light guide plate so that the straight component of light incident on the light guide plate is totally reflected in the light guide plate. By converting it into light, it can be used effectively, the light utilization efficiency can be improved, and a display device capable of visually displaying high-luminance display light can be obtained.

以下、本発明による導光板の実施形態を、図面を用いて詳細に説明する。
図２に示すように、光源１から導光板２に光が入射し伝播していくとき、伝播する光は、全反射条件を満たす角度で反射を繰り返して進んでいく。 Hereinafter, embodiments of a light guide plate according to the present invention will be described in detail with reference to the drawings.
As shown in FIG. 2, when light enters the light guide plate 2 from the light source 1 and propagates, the propagating light travels repeatedly with an angle satisfying the total reflection condition.

導光板２がアクリル樹脂からなる場合、その屈折率を約１．５とすると臨界角は４１．８°（≒４２°）であり、導光板の上面２１ａおよび下面２１ｂに４２°以上の角度で入射した光は全反射によって導光板内に閉じ込められ、伝播していく。   When the light guide plate 2 is made of acrylic resin, if the refractive index is about 1.5, the critical angle is 41.8 ° (≈42 °), and the upper surface 21a and the lower surface 21b of the light guide plate are at an angle of 42 ° or more. The incident light is confined in the light guide plate by total reflection and propagates.

しかし、光源から導光板に入射する光のうち最も強い直進成分７は、大部分がそのまま終端面から抜けてしまい、終端面近辺での輝度ムラの原因となる。
この直進成分７を有効に利用し輝度ムラを低減させるためには、図３に示すように直進成分７を終端面２２で回折させ、導光板下面２１ｂもしくは上面２１ａに全反射の条件を満たすよう臨界角４２°以上で入射させると良い。
そうすれば、直進成分７は内部で全反射を繰り返して伝播していくため、入射光と同様に導光板内に閉じ込めることができる。 However, most of the strongest linear component 7 of the light incident on the light guide plate from the light source passes through the terminal surface as it is, causing luminance unevenness in the vicinity of the terminal surface.
In order to effectively use the linear component 7 and reduce luminance unevenness, the linear component 7 is diffracted by the end face 22 as shown in FIG. 3 so that the light guide plate lower surface 21b or the upper surface 21a satisfies the condition of total reflection. It is good to make it incident at a critical angle of 42 ° or more.
Then, since the straight component 7 repeats total internal reflection and propagates, it can be confined in the light guide plate in the same manner as the incident light.

このように伝播していく際に、図４のように裏面のパターン３により散乱もしくは反射もしくは回折して導光板２の上面から適宜射出される。
このように、終端面から抜けてしまっていた直進成分を導光板上面からの射出光として利用することで、光の利用効率を向上させることができる。 When propagating in this way, the light is scattered, reflected or diffracted by the pattern 3 on the back surface as shown in FIG.
In this way, the light utilization efficiency can be improved by using the straight component that has been removed from the end surface as the light emitted from the upper surface of the light guide plate.

ここで、終端面２２に垂直に達する光の波長として、６３３ｎｍ（Ｒ）の光を想定する。
この光を終端面２２で回折した後、下面２１ｂで全反射させるためには、下面２１ｂに４２°以上の角度で入射しなくてはならない。
その際、終端面２２では４８°以下で回折させる必要がある。
このような条件を満たす回折格子パターンの空間周波数は、例えば４８°に回折させるときは約１２００本／ｍｍである。
空間周波数は以下の式で算出される。
ｄ＝λ／ｓｉｎθ
ｘ＝１／ｄ
ｄ；回折格子のピッチ幅
λ；光の波長
θ；回折格子への光の入射角度
ｘ；回折格子の空間周波数 Here, a light of 633 nm (R) is assumed as a wavelength of the light reaching perpendicularly to the end face 22.
In order for this light to be diffracted by the end surface 22 and totally reflected by the lower surface 21b, it must enter the lower surface 21b at an angle of 42 ° or more.
At that time, it is necessary to diffract the end face 22 at 48 ° or less.
The spatial frequency of the diffraction grating pattern satisfying such conditions is about 1200 lines / mm when diffracted at 48 °, for example.
The spatial frequency is calculated by the following formula.
d = λ / sin θ
x = 1 / d
d: Pitch width of diffraction grating λ: Wavelength of light θ: Light incident angle on diffraction grating x: Spatial frequency of diffraction grating

同様に、終端面２２に入射する光の波長として、５３２ｎｍ（Ｇ）の光を想定すると、４８°に回折させるのに必要な空間周波数は約１４００本／ｍｍである。
また同様に、終端面２２に入射する光の波長として、４４２ｎｍ（Ｂ）の光を想定すると、４８°に回折させるのに必要な空間周波数は約１７００本／ｍｍである。 Similarly, assuming that light having a wavelength of 532 nm (G) is incident on the end face 22, the spatial frequency required for diffracting to 48 ° is about 1400 lines / mm.
Similarly, assuming that light having a wavelength of 442 nm (B) is incident on the end face 22, the spatial frequency required for diffracting to 48 ° is about 1700 lines / mm.

図７に示すように、上記の３種類の空間周波数を持つ回折格子セルをマトリクス状に配置することにより、Ｒ，Ｇ，Ｂ成分から成る白色光を目的の角度で回折させることができる。
また、光源からの光の主成分が青と黄色の二種類の場合は二種類の回折格子セル、広い波長領域を有する光にはそれに含まれる波長成分に対応する回折格子セルを複数種類設けてもよい。 As shown in FIG. 7, white light composed of R, G, and B components can be diffracted at a target angle by arranging the diffraction grating cells having the above three types of spatial frequencies in a matrix.
In addition, when the main components of the light from the light source are two types of blue and yellow, two types of diffraction grating cells are provided. For light having a wide wavelength region, a plurality of types of diffraction grating cells corresponding to the wavelength components included therein are provided. Also good.

回折格子を断面鋸歯状のブレーズド格子にすることで、回折光の回折角を高効率かつ厳密に制御することができ、照明装置としての光の利用効率を一層高めることができる。   By making the diffraction grating a blazed grating having a sawtooth cross section, the diffraction angle of the diffracted light can be controlled with high efficiency and strictly, and the light use efficiency as the illumination device can be further enhanced.

このような回折格子パターンの作成は、例えば以下のようにして行われる。
ガラス基板などの上に記録材料層を形成したものに、電子ビームによって回折格子を描画することによって、任意の空間周波数の回折格子セルを描画することができる。 Such a diffraction grating pattern is created as follows, for example.
By drawing a diffraction grating with an electron beam on a recording material layer formed on a glass substrate or the like, a diffraction grating cell having an arbitrary spatial frequency can be drawn.

上記のように作成した回折格子パターンを成形時に側面加工する。
終端面２２に回折格子パターンを配置することにより、光の利用効率を向上させることができるが、さらに利用効率を高めるために反射板もしくは金属蒸着層を設けてもよい。
金属反射では光吸収が若干生じるが、回折格子パターンを配置しても生じてしまう終端面における光の抜けを大幅に削減することができるため、光吸収を考慮しても全体の光の利用効率は向上する。 The side surface of the diffraction grating pattern created as described above is processed during molding.
The use efficiency of light can be improved by arranging the diffraction grating pattern on the end face 22, but a reflector or a metal vapor deposition layer may be provided to further improve the use efficiency.
Light absorption occurs slightly with metal reflection, but light leakage at the end face that occurs even when a diffraction grating pattern is placed can be greatly reduced, so the overall light utilization efficiency even when light absorption is considered Will improve.

もしくは、さらに光の利用効率を高めるために、終端面２２に傾斜角をつけてもよい。
図５に示すように、全反射条件を満たす角度（４２°以上）で直進成分７が終端面２２に入射するようにすれば、終端面２２からの抜けをなくすことができる。
このとき、図６に示すように、傾斜角を考慮した上で回折格子を設計し終端面に配置し、終端面での抜けを防ぐと共に、導光板下面２１ｂもしくは上面２１ａに臨界角４２°以上で入射させるようにすれば、光の利用効率をさらに高めることができ、望ましい。 Alternatively, in order to further improve the light utilization efficiency, the end face 22 may be inclined.
As shown in FIG. 5, if the rectilinear component 7 is incident on the end surface 22 at an angle satisfying the total reflection condition (42 ° or more), the omission from the end surface 22 can be eliminated.
At this time, as shown in FIG. 6, the diffraction grating is designed in consideration of the inclination angle and disposed on the end surface to prevent the end surface from coming off, and the light guide plate lower surface 21b or upper surface 21a has a critical angle of 42 ° or more. In this case, it is desirable that the light utilization efficiency can be further increased.

従来技術に係るバックライト・ユニットの概要を示す断面図。Sectional drawing which shows the outline | summary of the backlight unit which concerns on a prior art. 光源からの入射光が導光板内へ入射し、導光板内で伝播する挙動を説明する概念図。The conceptual diagram explaining the behavior which the incident light from a light source injects into a light guide plate, and propagates in a light guide plate. 本発明による導光板の概要を示す断面図であり、導光板の終端面で伝搬した光が回折され、導光板内を戻って伝播する挙動を説明する概念図。It is sectional drawing which shows the outline | summary of the light-guide plate by this invention, and is the conceptual diagram explaining the behavior which the light propagated on the termination | terminus surface of the light-guide plate is diffracted, and propagates back in the light-guide plate. 本発明による導光板で、導光板内を戻って伝播する光が回折される挙動を説明する概念図。The conceptual diagram explaining the behavior in which the light propagating back in the light guide plate is diffracted by the light guide plate according to the present invention. 本発明による導光板の別実施形態に係る概要と、導光板の終端面で伝搬した光が回折される挙動を説明する概念図。The conceptual diagram explaining the outline | summary which concerns on another embodiment of the light-guide plate by this invention, and the behavior by which the light which propagated on the termination | terminus surface of a light-guide plate is diffracted. 本発明による導光板の別実施形態に係る概要と、導光板内を戻って伝播する挙動を説明する概念図。The conceptual diagram explaining the outline | summary which concerns on another embodiment of the light-guide plate by this invention, and the behavior which propagates back in the light-guide plate. 本発明における、終端面に設ける回折格子の構造例を示す平面図。The top view which shows the structural example of the diffraction grating provided in a termination | terminus surface in this invention.

符号の説明Explanation of symbols

１：光源
２：導光板
２１ａ：導光板上面
２１ｂ：導光板下面
２２：終端面
３：ドットパターンもしくはプリズムパターンもしくは回折格子パターン
４：反射シート
５：拡散シート
６：プリズムシート
７：入射光の直進成分 1: Light source 2: Light guide plate 21a: Light guide plate upper surface 21b: Light guide plate lower surface 22: Termination surface 3: Dot pattern or prism pattern or diffraction grating pattern 4: Reflective sheet 5: Diffusion sheet 6: Prism sheet 7: Straight traveling of incident light component

Claims (7)

導光板の一方の端面に光源を配し、前記導光板に入射した光を均一に上面へ反射させて面光源とするエッジライト方式のバックライト・ユニットに用いられる導光板において、
光源と反対側の端面である終端面は、前記光源から入射した光の直進成分の光を４２°以上で前記導光板上面もしくは前記導光板下面に入射させるように、傾斜角をつけた構成であり、かつ、前記終端面には反射型回折格子が配置されていることを特徴とする導光板。 In the light guide plate used in the edge light type backlight unit, a light source is arranged on one end surface of the light guide plate, and the light incident on the light guide plate is uniformly reflected on the upper surface to be a surface light source.
The termination surface , which is the end surface opposite to the light source, has a configuration in which an inclination angle is provided so that light of a linear component of light incident from the light source is incident on the upper surface of the light guide plate or the lower surface of the light guide plate at 42 ° or more. And a reflection type diffraction grating is arranged on the end face . 前記回折格子が、表面レリーフ型であることを特徴とする請求項１記載の導光板。 The light guide plate according to claim 1, wherein the diffraction grating is a surface relief type. 単一の空間周波数の回折格子から成る小領域を回折格子セルとし、空間周波数の異なる複数種類の回折格子セルが、前記導光板の終端面にマトリクス状に配列された構成であることを特徴とする請求項１または２に記載の導光板。 A small region consisting of a single spatial frequency diffraction grating is used as a diffraction grating cell, and a plurality of types of diffraction grating cells having different spatial frequencies are arranged in a matrix on the end face of the light guide plate. The light guide plate according to claim 1 or 2. ３種類の回折格子セルが規則的に配置され、各回折格子セルの空間周波数がＲ，Ｇ，Ｂの波長に対して設計されていることを特徴とする請求項３記載の導光板。 4. The light guide plate according to claim 3, wherein three types of diffraction grating cells are regularly arranged, and the spatial frequency of each diffraction grating cell is designed for wavelengths of R, G, and B. 前記回折格子が、断面が鋸歯状のブレーズド格子であることを特徴とする請求項１〜４の何れかに記載の導光板。 The light guide plate according to claim 1, wherein the diffraction grating is a blazed grating having a sawtooth cross section. 回折格子には、少なくとも何れかの表面に光反射層を形成するか、もしくは回折格子に近接させて光反射体を配置した構成であることを特徴とする請求項１〜５の何れかに記載の導光板。 6. The diffraction grating according to claim 1, wherein a light reflection layer is formed on at least one surface of the diffraction grating, or a light reflector is disposed close to the diffraction grating. Light guide plate. 請求項１〜６の何れかに記載の導光板の一方の端面に光源を配し、前記導光板に入射した光を均一に上面へ反射させて面光源とするエッジライト方式のバックライト・ユニットを具備する構成の表示装置。An edge-light type backlight unit in which a light source is disposed on one end face of the light guide plate according to any one of claims 1 to 6, and light incident on the light guide plate is uniformly reflected on an upper surface to be a surface light source. A display device comprising:
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